1. Field of the Invention
The invention relates to ground penetrating radar (GPR) systems, and more specifically to a new method for identification of buried objects and structures with the help of a GPR system.
2. Description of the Related Art
Unlike upward-looking radar used for air traffic control and meteorology, the antenna in a ground penetrating radar (GPR) is directed downwards into the ground. For example, GPR is used for geophysical applications such as mapping subsurface strata, locating toxic waste sites for remediation, detecting of unexploded subsurface ordinance and locating pipes and cables.
A GPR system comprises at least one transmitter that transmits an electromagnetic impulse, usually in the frequency range of 1 MHz to 10 GHz. The system also comprises at least one receiver that receives a reflected waveform. The length of the impulse is usually adjusted to match the desired frequency range. The desired impulse duration may be expressed approximately in nanoseconds(ns) as 1/f, where f is the centre frequency in Gigaherz (GHz). Therefore, a 1 GHz antenna is fed with an impulse of 1 ns duration, a 500 MHz antenna is fed with an impulse of 2 ns duration, and a 100 MHz antenna is fed with an impulse of 10 ns duration. Ideally, this gives the transmitted waves very broad frequency content, centred around the frequency f. In practice the transmitted pulse is between 1 and 2 cycles of the centre frequency. Therefore, GPR systems are sometimes referred to as xe2x80x9cimpulsexe2x80x9d or xe2x80x9cultra wide bandxe2x80x9d (xe2x80x9cUWBxe2x80x9d) radars.
Subsurface applications such as construction, utility locating, environmental remediation, and unexploded-ordnance detection have long sought safe, reliable, cost-effective methods for xe2x80x9cseeing into the groundxe2x80x9d. The utility locating market suffers greatly from inadequate locating technologies that results in hundreds of millions of dollars in damage, delays, and lost revenue for locating companies and contractors every year, losses that could be significantly reduced if GPR could be made an standardised method in these applications.
A big advantage of GPR, compared with other locating technologies, is that it can detect non-metallic as well as metallic objects. One other significant advantage with GPR is that it is not dependent on a metallic target that is unbroken, it can detect a broken cable equally as well as an unbroken cable. Other technologies that are used for locating purposes lack the ability to locate non-metallic utilities and have problems locating electrically broken metallic (cables and pipes) utilities.
GPR is used, to a limited extent, today for utility locating. The reflected waveforms are filtered and processed to an image that are displayed on a laptop-computer or some other display device. These display devices often have very poor performance in outdoor daylight, where most of the fieldwork has to be done. An important reason why GPR has not been accepted as a standardised method is that these images are difficult to understand and thus need to be interpreted by a qualified person. If a person not skilled in the art of interpreting radar images makes interpretations, the failure rate becomes too high. For this reason radar surveys are usually performed by consulting companies with qualified personnel, such as geophysicists or specifically trained geologists. Even for the qualified experts the processing and interpretation of data from a GPR system is cumbersome and time-consuming. This makes the GPR technology too costly for broad use in the utility locating industry. There is thus a need for better methods for utility locating.